Field of the Invention
The present invention relates to a work vehicle and a work vehicle control method for charging.
Background Information
Work vehicles, such as wheel loaders, are known that are equipped with a power transmission device that includes a torque converter and a multi-speed transmission (hereafter referred to as a “torque converter transmission”). Recently, on the other hand, the hydraulic mechanical transmission (HMT) and the electro-mechanical transmission (EMT) have been replacing torque converter transmissions as power transmission devices.
As disclosed in Japanese Laid-Open Patent Application Publication No. 2006-329244, an HMT includes a gear mechanism and a motor connected to the rotational elements in the gear mechanism, where a portion of the drive power from the engine is converted to hydraulic pressure and transmitted to the travel apparatus while the remainder of the drive power is mechanically transmitted to the travel apparatus.
An EMT is provided with a planetary gear mechanism and an electric motor, for instance, to allow for continuously variable shifting. One of three elements, i.e., the sun gear, the carrier, or the ring gear in the planetary gear mechanism is connected to an input shaft, and a second element is connected to an output shaft. Additionally, a third element is connected to the electric motor. The electric motor functions as either a motor or a generator depending on the travel status of the work vehicle. In an EMT the rotation speed of the output shaft varies continuously in accordance with the variation in the speed of the electric motor.
The HMT uses a hydraulic motor in place of the electric motor in the EMT. The hydraulic motor functions as either a motor or a pump depending on the travel status of the work vehicle. Similar to the EMT, the rotation speed ratio of the output shaft to the input shaft varies continuously in accordance with the variation in the rotation speed ratio of the hydraulic motor.